Accessing clients web without domain

Is it possible to access a clients web without a domain connected to it?

Szenario:
Before we transfer a clients domain to the new host, we want to make sure that their web is running with the uploaded CMS (in this case typo3).
So the clients domain (e.g www.client.tld) is pointing to the old host at the moment.
How can we access the clients webpage at the new host (running with ISPConfig)?